Twitter has acknowledged that it stores user data – including info from contact lists and address books – on its servers, sometimes for months at a time.

At issue is a mobile feature called Find Friends, which allows smartphone users to locate real-life friends on Twitter. Results are produced by giving Twitter permission to churn through the contacts on your phone. So far, so good.

But after critics raised questions about the functionality, Twitter confirmed that the data was not immediately erased – instead, all of it, including phone numbers and email addresses, remained on Twitter servers for up to 18 months.

In a statement, Twitter has promised more clarity on existing privacy policies.

"We want to be clear and transparent in our communications with users," a Twitter spokesperson told the LA Times. "Along those lines, in our next app updates, which are coming soon, we are updating the language associated with Find Friends – to be more explicit. In place of 'Scan your contacts,' we will use 'Upload your contacts' and 'Import your contacts' (in Twitter for iPhone and Twitter for Android, respectively)."

According to the Register, Privacy International has encouraged Twitter users to obtain copies of all the data Twitter has collected about them. "We hope that by raising awareness we can also gain clarity on what information Twitter collects and stores about its users," the group said, "especially after the recent news that Twitter has been storing the full iPhone contact lists of users who choose to 'Find Friends'."

In related news, back in January, Twitter announced that it would invoke the right to censor messages on a country-by-country basis. In the past, Twitter was forced to strike clean objectionable tweets on a "global" scale – the offending message, in other words, would disappear across the board. Twitter reps claimed it changed its policy to abide by the laws of "countries that have different ideas about the contours of freedom of expression."